So we have progressed enough in science now to know beyond reasonable doubt that life can develop on any planet given the right set of circumstances.
The high number of planetary systems in the universe leads one to assume that it is likely there has been life elsewhere in the universe or will be in the future.
On the other hand, the difference between the time that life has existed on earth, and the time that the universe has existed means it seems unlikely that the same has happened at the same time elsewhere in the universe.
So what are the best mathematical workings out that have been done for the following…
That intelligent life has existed elsewhere.
That intelligent life exists elsewhere now.
That intelligent life exists elsewhere now and will some day come into contact with ourselves.
And fourthly, all of the above without the word ‘intelligent’ (because life is more likely than intelligent life)
It’s tangentially related, but you might be interested in the Drake equation I’d hardly call it useful, and I really doubt you’ll come up with anything more than complete WAGs.
We use this as an assumption, but nothing is known beyond reasonable doubt about the development of life and the evolution of intelligent life. We have one example and extrapolation is meaningless from a sample size of one.
Snarky_Kong correctly identifies the Drake equation as a purported mathematical starting point and correctly points out that most scientists consider it a joke.
You can plug in any numbers you like and be as right as anybody else. We just don’t know enough about anything to make any meaningful statements on the subject. Come back in a hundred years and ask again.
Assuming the simplest cosmological models consistent with current evidence, the answer to all of your questions is 100%. The number of stars in the Universe appears to be infinite, while all other factors in the Drake equation are finite, so there should be an infinite number of other intelligent civilizations in the Universe.
The question, then, is just one of how far away they are. It’s still quite possible that our nearest neighbors are so far away that there’s no hope of ever communicating with them, which makes them somewhat irrelevant.
We do not, in fact, know this. We know that the fundamental proteins needed for terrestrial life are not rare, and that conditions that would support some kind of primitive life probably exists in a non-statistically-significant number of planets. We do not, however, know how the process of going from self-catalyzing enzymes (the likely progenitor of life) to a true, independently self-replicating, metabolic organism occurred or how it can be made to occur again.
Even if we establish that the abiogenesis of life is a relatively common event (and I suspect that it is), the development of specialized multicellular non-colonial organisms (and the apparently necessary integration of endosymbiotic organelles into such in order to support the highly energetic metabolism required) follows a chain of statistically limited events. As such, complex organisms akin to what we would consider intelligent or even on par with the simplest plant or animal requires an unlikely chain of events. The only saving grace is that there is a phenomenal number of chances for this to occur, but in absence of more data than just one “set” of life, we can’t really assess a likelihood for intelligent life to arise in the same domain of time and relative locality to us.
Well, it’s bigger than we can observe, anyway, at least assuming that we don’t find any repetition or overlap in WMAP data. That makes it effectively infinite, though there is definitely a finite portion of it that we can observe, and an even more limited that we can possibly ever reach without Hollywood sci-fi technology.
I don’t think “effectively infinite” is a meaningful term, especially in the context of Chronos’ post where he used the infinite number of stars to obtain a 100% solution to the Drake Equation.
Even given infinitely many stars, some of those other factors could be 0, giving us an indeterminate form for the final product, allowing anything from 0 to 100% and inbetween.
For that matter, some of those other terms might not be all that well-defined when one starts looking at averages involving ratios of infinite quantities.